They are not the most lethal force in Ousen's army because each invidual of them is good 1 vs 1 combatant but rather because they work very well as a squad,Sanchuu as a human shield to use to block the enemy's strikes and distract him while the other 2 to sneak attack and deliver a killing blow.
Together,they prove that they can take down Ji Aga's level warrior if they caught him off guard,Honestly,if they caought their enemy off guard they can problay take down any great general's martial vassal with the exeption of zenou.
As how good they are in 1 vs 1 combat,SBS one shot The Duke(who seem the strongest)without even noticing that he wasn't some fodder soldier but an elite unit. the moment kansaro was serious/mad,he took down the other 2 easly.
In 1 vs 1,they may not even be an akakin level,best i give them is arnoud Kanjou's Level.